Turbocharging carburated motorbike engine.

[half-fast]

I too tried the RHB-31 with a 38MM mikuni in suck through configuration on a single cylinder. I would like to know where you acquired a RHB-31 from.

Like others have said, I have experienced first hand destroying the turbo due to oil seal issues, and would suggest running both a separate supply pump and scavenge pump with a separate reservoir for the turbo. I also firmly believe as others have said, that a single cylinder does not lend itself to turbo'd applications because the exhaust pulses are too few and too weak to really make the turbo shine, also consider the pulsations occurring when the intake valve opens and the cylinder is charged, some have suggested a plenum that is at least as big as cylinder volume, of course this leads to the inherent drawbacks of fuel mixing etc with a suck through system, we also tried a BIG turbo on a small 2 cycle and came to the same conclusion that a turbo hurts naturally aspirated performance on small displacement single cylinder engines.

That being said, I intentionally ran the motor way rich, and WFO throttle was the worst performing area by seat of the pants feel, feels like the motor is way too restricted, which it probably is by exhaust backpressure, (using a factory cam). For the fire out of the dump pipe, try retarding the timing a bit, and watch for the turbo oil seals to go away. Install an O2 sensor with meter in the header pipe and take it out for a spin, be leery of plug checks because of oil contaminating the intake charge.

In a perfect world, a blow through, with intercooling and big plenum, is the way to go, but still think the exhaust issues are relevant with a single cylinder

Hope it helps

[moirmyster]

thanks for that very interesting.im running 400cc plentum chamber as hav read needs to be double the displacment of the engine.
That was my next thort was the engine to restriced needing over size valves some porting as the exhust port is quite small.
Seems to move enough exhuast gases to spool up turbo.
so what is installing a O2 sensor gonig to tell me.
I got the turbo off trademe.co.nz is a trading site in new zealand.
i beleve the turbo is of a suzuki cappacino 600cc car.

I also for got to mention it gets full throttle fine when not under load may make sence to some one.

I had a similar problem.
Ran great until the throttle was wide open.
I my case it was too small of hotside.

Sam

So i guessing u mean that it may need a bigger dump pipe.

Thanks
scotty

[kiwi]

Anyone know if compressor surge could cause the problem?

[moirmyster]

ok so i mucked around today i fitted air filter on it that has seemed to hav fixed the problem something so simple,i didnt think it needed one as thort it needed to suck as much air as poss.
not sure it goes any faster,sounds fast tho lol.
thanks for everyones help,learnt lots.

cheers
scotty

[joea]

too small a hot side means too small on the turbine side........

there is no way an engine should make around the same hp
if making positive manifold pressure....and supplying additional
fuel..........

[moirmyster]

yea thats true thats what i throught to,if it is any faster maybe like 2 to 5 hp.would need to dyno it or hav a drag with a stock one.
The next thing im going to do is open up the ports,make it flow better im sure that will be a good increase in power.

[half-fast]

too small a hot side means too small on the turbine side........

there is no way an engine should make around the same hp
if making positive manifold pressure....and supplying additional
fuel..........

I am no Smoky Yunick, and would agree unless increasing intake manifold pressure and additional fuel result in efficency decreases, from say pumping losses, (which I hypothesize as quite big on a single cylinder turbo) and positive pressure exhaust during valve overlap.

[Dakin Engineering]

A bit of clarification; The hot side intake was smaller than the exhaust pipe. Like trying to exhale thru a straw. Actually made less power than NA.  An "expert", who shall remain nameless, claimed it was the perfect size turbo for a sub-liter engine.

The early boost caused a reversion wave out the carb that I could smell at 60 mph. I can imagine holding the throttle open long enough to nearly drown the spark and a flamethrower exhaust. Just a guess.

Sam

[moirmyster]

bike is going great still bit of fine tunning but getting there.
ok my next problem is its sucking oil past the seals like i was told it would.
I dont no much about turbos but i pulled to bits looks pretty simple,i was expecting to c some sort or rubber seal but the was just some special seal that clips in strange,doesnt even look like a seal.
How can i fix this problem is there a special seal u can get.

[maj]

Hope you marked the relationship of compressor wheel to shaft or your balance will be out on reassembly.
Piston ring type seal std, you need a spring loaded carbon seal , sort of thing common in water pumps

[moirmyster]

Hope you marked the relationship of compressor wheel to shaft or your balance will be out on reassembly.
Piston ring type seal std, you need a spring loaded carbon seal , sort of thing common in water pumps

No i didnt mark it,do u hav to hav a special michine to balance it,by the looks of it some butcher had already been in there,wether he markrd if not dont no.
Ok cool thanks for that ill have to try track that seal down.

[moirmyster]

ok so iv got this bike going really good now,i ported the head and oversize valves,has got heaps more power than a stock one.my problem now is its getting to hot as its making more power.Its hard to keep cool as its air cooled engine.i raced it the other day for about 10 mins and it got that hot it nipped up,let it cool down and its away again.the engine hasnt got a oil cooler so the only thing i could think off is some how hook one up,like with a external oil pump.
has any one got any suggestions.

[Queeziryder]

Hi you're going basically the right way, and with a few hints I dont forsee to many problems ahead.

On my old Kwak funny bike I used to run the turbo oil system completely independant of the bike, so that I couild control, both the flow and pressure to the turbo. I used a MOCAL external 12V oil pump which gave me the flow, but to much pressure, so I made up my own spring loaded bypass valve. I ended up with around 45 PSI and it would circulate the 2.5 Litre oil capacity in approx 15 secs. You need to make the bore of the return pipe at least 3 times the feed pipe, so that there is no oil pressure build up within the turbo, otherwise this can make any leak past the seal worse.  Run high quality synthetic oil for the turbo, such as Mobil1 0W40.

With regard to the exhaust side of things, you want a reasonably large bore pipe from the port to the turbo, and a VERY large pipe on the output and wastegate from the turbo, otherwise you will increas the back pressure to much.

If you cant get a copy of the Mcinnes book let me know, and I can scan in some pages for you..


Neil

[McRat]

Roller bearing motorcycle engines do not put out enough oil pressure or volume to feed a plain-bearing charger.  You want at least 15psi oil pressure at idle for the turbo, and if I remember right, a roller-bearing bike only gets about 8 psi at idle.  If you must run from the factory engine oil pump, you should only use a roller-bearing charger.

[Boostedballs]

Does the carb have a power valve? If it does, you'll have to plump the vac line to the pressure section of the compressor. If not. you will be messing with jets until the cows come home. It bothers me that it runs better with the air cleaner on. When you go WOT after idle and it bogs under load but not off-load; this tells me you don't have enough fuel for the transition. You should get the bike on a dyno with a thermocouple and WIDE-band O2 in the exhaust. Weld your fitting UPSTREAM of the turbo so you don't get weird readings from oil passing the turbo seals.
The turbine inlet needs to be the same size as the exhaust port and tubing. The turbines usually have enough material that you can hog it out a little to get a nice transition. Keep the exhaust moving fast! It sounds like your intake plenum is plenty; that's the area where most of the Harley guys screw up. Extra length in the exhaust between port and turbine might be a good thing.
I hope you are running 2 steps colder on the plugs.
Water injection does great things for air-cooled turbo engines. That can be as simple as a small ABS plastic tank with a valve stem, filter (inside, so it doesn't have to be a high pressure unit), a hobs switch or WOT switch, solenoid and fogger nozzle. Fill it 1/2 full of -40F or -30F windshield washer fluid and then pump to 100+ psi. Vent it when the bike is off.
Nozzle sizing should be calculated so you are giving the engine 1:4 or 1:5 water:fuel.
The water injection will keep the head cooler, allow more timing and it'll keep your combustion chambers clean.